Journal of Entomology and Zoology Studies 2014; 2 (4): 35-41
ISSN 2320-7078 JEZS 2014; 2 (4): 35-41
© 2014 JEZS Received: 14-06-2014 Accepted: 23-06-2014
Srinath B S
Department of Zoology, Karnatak University Dharwad, India N Shivanna
Department of Applied Genetics, Karnatak University Dharwad, India
Correspondence:
N Shivanna
Department of Applied Genetics, Karnatak University Dharwad, India.
Seasonal variation in natural populations of Drosophila in Dharwad, India
Srinath B S, N Shivanna
ABSTRACT
Drosophila flies were collected in and around Dharwad district during different seasons of 2011 and 2012.
A total of 13853 individual flies comprising of 20 different species were collected by bottle trapping and net sweeping method. Maximum number (19) of species was recorded during monsoon 2012 and minimum number of species (5) during winter 2012 Statistical analysis revealed a positive correlation between abundance and average rainfall. No correlation was observed between abundance and temperature. The diversity of species was more during post-monsoon 2012 and less during winter 2012.
Their abundance cluster analysis revealed three clusters where D. malerkotliana, D. bipectinata, D. nasuta nasuta and Phorticella striata are predominant species. D. eugracilis, D. jambulina, D. rajasekari, D.
sulfurigaster neonasuta and D. ananassae are intermediate species whereas remaining 11 species are less dominant species.
Keywords: Biodiversity, Drosophila, Dharwad, seasonal variation, diversity indices, cluster analysis.
1. Introduction
Drosophila has been considered as a model system in the studies of genetics, evolution and ecology. There are about 65 genera classified under Drosophilidae family which is composed of more than 3,500 described species that occur in diverse ecosystems all over the world [15]. Some species are endemic to certain regions and few are cosmopolitan. These insects are highly sensitive to environmental variations which lead to fluctuation in their size of natural population.
Studies on the population structure and ecology of Drosophila species have provided important information in understanding their evolutionary process [2].
Studies on seasonal variation of Drosophila in different parts of the world have been carried out by earlier workers like Dobzhansky and Pavan [5] from Brazil; Paik [18] from South Korea and Wakahama [31] from Japan. Torres and Madi Ravazzi [29] have studied seasonal variation of Drosophila from Sao Paulo, Brazil. In India Parshad and Paika [19] have studied the effect of seasonal variation on Drosophila population from Punjab. Hegde et al. [11] have reviewed biodiversity, eco distributional pattern and seasonal variation of Drosophila species in South India. According to them out of 140 species in India, South India has 50 species. Most of the Drosophila diversity studies were concentrated on surrounding areas of Mysore in South Karnataka [25] and North Kanara district in northern part of Karnataka [17, 30] and the Western Ghats [22, 23, 24]. Most of the studies have revolved around altitudinal variation in relation to rainfall and temperature [7, 21, 8, 9, 10]. Recently Srinath and Shivanna [27] reported a variant of rare species D. daruma belonging to Polychaeta subgroup of the genus Drosophila from Kalghatgi forests of Western Ghats of South India. Seasonal variation studies on Drosophila of South India are fragmentary and poorly understood. In view of this, the present work has been undertaken to study the effect of seasonal variation on Drosophila species of Dharwad district.
2. Material and methods 2.1 Study area
Dharwad district is situated in the western sector of the northern half of Karnataka state. It lies between the latitudinal parallels of 15° 15' and 15° 35' North and longitudes of 75° 00' and 75°
20' East with an area of 4, 27,329 ha out of which 8.24% of land area is under forest. The district lies approximately about 800 meters above sea level, which is the reason for a moderate and healthy climate. The annual rainfall in the district ranges from 998.2 to 594.30 mm. Dharwad district is divided into 5 taluks Dharwad, Hubli, Kalghatgi, Kundagol and Navalgund.
Physiographical status of Dharwad falls within the macro region of Deccan Plateau.
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The district is classified into two prominent landscapes: the Dharwad and the black soil plains. The Dharwad landscape which features Sahyadrian region of the western belt of the district covers the Kalghatgi taluk. The landscape is marked by chain of low hill ranges. The landscape of black soil plains on this Sahyadrian region constitute a transitional belt where the hilly landscape of the west passes into the undulating plain of black soil. The forest land is concentrated in Kalghatgi taluk (28.39%), Dharwad (12.23%) and Hubli (2.75%) taluks. There is no forest land in Kundagol and Navalgund taluk. Monsoon deciduous forests are found in the Malnad zones which include Kalghatgi and Dharwad (Part of it) taluks [16]. On an average the western region of the district receives more rainfall than the eastern plains.
2.2 Collection and Sampling method
Flies were collected using both bottle trapping and net sweeping methods as mentioned by Hegde et al. [11]. Bottle trapping was done using 200 ml milk bottles filled with banana smash tied to trees at least two and half feet above the ground and left open for 24 to 48 hours. It was plugged with cotton before collection. The bottles were tied to trees where there was minimum exposure to sunlight especially during summer and monsoon. Care was taken to avoid rain entering the bottles as they get filled with water and flies collected from such bottles get stuck in the fruit media and are dead by the time they are brought to the laboratory. Net sweeping method was done by spreading the fruits on the ground under cool shaded areas. Sweeping was done after 24 to 48 hours of spreading.
Collection of flies was done during morning hours and the temperature was recorded.
A total of 8 bottles were tied per site for collection during each season. The trapped flies were brought to the laboratory and segregated according to their sex. Individual females were cultured in vials containing wheat cream agar medium [26]. The male flies were identified and recorded according to Hsu [12], Bock and Wheeler [3], Grimaldi [6] and Markow and O’ Grady [14]. Collection of flies was done from different localities such as the Western Ghat forests of Kalghatgi and Dharwad, fruit markets of Hubli and Dharwad, Mango and Guava orchards, residential areas and agricultural fields of all the 5 taluks. Drosophila flies were collected during different seasons of 2011 and 2012. The seasons were divided according to meteorological department of India as winter (January to February), summer (March to May), monsoon (June to September) and post-monsoon (October to December).
The rainfall data was obtained from the meteorological department of India (available online http://www.imd.gov.in).
The relationship between the abundance of individual species, average rainfall and temperature was analysed for different seasons
by means of the Spearman correlation coefficient (r) [29]. Diversity of the flies during different seasons and of different taluks was calculated using Simpson Index (1-D), Shannon index (H) and Equitability index (J) using PAST 3.X software [15, 9]. Simpson Index was calculated to analyze the probability that two individuals randomly selected from a sample belong to the same species.
Formula to calculate Simpson index is D = 1- ∑ni (ni-1)/N (N-1) where ni = the total number of organisms of particular species; N=
the total number of organisms of all population. Shannon index was calculated using the formula H' = -ln ∑pi ln pi where pi = proportion of individuals belonging to the same species in a given sample. The equitability index was also calculated using the formula J|= - ln ∑ pi
ln pi / ln N. This is the Shannon Weiner diversity Index divided by ln N. This index measures the uniformity or equity of the species distribution [13].
SPSS 16.0 statistical package was used to determine the level of similarity of the 20 species of Drosophilids obtained and hierarchical cluster analysis (Euclidean distances, Ward’s method) was used to construct a single linkage dendrogram. Cluster analysis is a technique used to classify cases into groups that are relatively homogeneous within themselves and heterogeneous between each other.
3. Results
Table 1 shows the number of Drosophila species collected in and around Dharwad district during different seasons of 2011 and 2012.
It revealed that 13853 individual flies were collected consisting of a total of 20 species; among which, 11 species belonged to subgenus Sophophora, 4 belonged to subgenus Drosophila, and 2 belonged to genus Scaptodrosophila, while one species each belonged to genus Zaprionus and Phorticella respectively.
Maximum flies were obtained during monsoon 2012 whereas minimum flies were obtained during winter 2012. D. malerkotliana and D. bipectinata were found to be abundant during monsoon, followed by D. n. nasuta and P. striata. During summer, P. striata was abundantly found. During post-monsoon, D. n. nasuta was found dominant followed by D. malerkotliana and D. bipectinata.
During winter D. ananassae was dominant species. D.
melanogaster, D. ananassae, D. malerkotliana and P. striata were found in all the seasons. Rare species such as D. punjabiensis, D.
bhagamandalensis, and D. daruma were found only during monsoon and post-monsoon season whereas D. latifshahi was found during summer 2012 season. The abundance of Drosophila population varied for different seasons. Drosophila population size was found to be maximum during monsoon and minimum during winter.
Table 1: Seasonal variation of Drosophila in Dharwad District collected during 2011-12 season
Species Winter
2011
Summer 2011
Monsoon 2011
Post- monsoon
2011
Winter 2012
Summer 2012
Monsoon 2012
Post- monsoon
2012
Total Genus Drosophila
Subgenus Sophophora melanogaster subgroup
Drosophila melanogaster 12 15 65 11 14 8 82 24 231 ananassae subgroup
D. ananassae D. malerkotliana
D. bipectinata
121 18
3
273 64 53
206 1186 1314
41 196 167
86 8 --
211 46 35
148 1405 1398
25 155 117
1111 3078 3087
suzukii subgroup
D. rajasekarii -- 42 187 30 -- 17 234 10 520 eugracilis subgroup
D. eugracilis -- 2 82 136 -- 7 67 112 406 montium subgroup
D. kikkawai D. jambulina D. punjabiensis D. bhagamandalensis
6 -- -- --
7 12
-- --
18 114
2 4
25 65 -- 5
-- -- -- --
3 16
-- --
34 178
3 3
15 34 -- 4
108 419 5 16 takahashii subgroup
D. takahashii -- -- 5 -- -- -- 6 2 13 Subgenus Drosophila
immigrans group D. nasuta D. neonasuta
20 --
39 3
447 289
152 48
12 --
76 14
762 133
178 88
1686 575 repleta group
D. repleta 8 13 17 2 -- 21 21 13 95 Polychaeta group
D. daruma*
D. latifshahi*
--
-- --
-- --
-- --
-- --
-- --
3 3
-- --
-- 3
3 Genus Scaptodrosophila
Scaptodrosophila nigra S. krishnamurthyii
--
-- 12
4 34
7 --
-- --
-- 4
15 24
4 --
-- 74
30 Genus Zaprionus
Zaprionus bogoriensis 18 10 48 2 -- 13 73 13 177 Genus Phorticella
Phorticella striata 13 237 776 78 9 337 681 85 2216
Total 219 786 4801 958 129 826 5259 875 13853
Average rainfall (in mm) Average temperature (0C)
3.85 23.5
37.4 27.5
112 24
56.9 25
0.0 23.5
22.8 27
70.9 24.5
40.6 26.5 Source: Classification according to Hsu (1949); Bock and Wheeler (1972); Grimaldi (1990) and Markow and O’ Grady (2006)
* Rare species collected for first time from South India
Figure 1 revealed that there was a positive correlation between average rainfall and abundance of the species (r = 0.952).
Fig 1: Correlation between average rainfall and population abundance of Drosophila during 2011-12 seasons.
The correlation coefficient analysis for individual species revealed that out of 20 species about 12 species showed positive correlation with rainfall (Table 2).
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Table 2: Correlation coefficient (r) value of individual species of Drosophila against average rainfall for 2011-12 season
S. No. Species r value
1 Drosophila melanogaster 0.595
2 D. ananassae 0.048
3 D. malerkotliana 0.976**
4 D. bipectinata 0.976**
5 D. rajasekari 0.850**
6 D. eugracilis 0.778*
7 D. kikkawai 0.905**
8 D. jambulina 0.946**
9 D. punjabiensis 0.733*
10 D. bhagamandalensis 0.779*
11 D. takahashii 0.764*
12 D. nasuta 0.929**
13 D.s. neonasuta 0.946**
14 D. repleta 0.494
15 D. daruma 0.412
16 D. latifshahi -0.247
17 Scaptodrosophila nigra 0.634
18 S. krishnamurthyii 0.345
19 Zaprionus bogoriensis 0.551
20 Phorticella striata 0.762*
* Significant at 0.05 level, ** Significant at 0.01level
The correlation coefficient between temperature and abundance of species was not found significant (Fig. 2)
Fig 2: Correlation between average temperature and population abundance of Drosophila during 2011-12 seasons The Simpson index of diversity and Shannon index calculated for
different seasons revealed that post-monsoon 2012 were more diverse whereas winter 2012 was less diverse. Post-monsoon 2011
had more values for equitability index whereas summer 2012 revealed less values (Table 3).
Table 3: Diversity indices values calculated for Seasonal variation of Drosophila during 2011-12 Seasons No. of species recorded Simpson index Shannon index Equitability index
Winter 2011 9 0.6641 1.562 0.7109
Summer 2011 15 0.7706 1.852 0.684
Monsoon 2011 18 0.8155 2.011 0.6957
Post-monsoon 2011 14 0.865 2.178 0.8253
Winter 2012 5 0.6454 1.09 0.6775
Summer 2012 16 0.7524 1.838 0.6628
Monsoon 2012 19 0.815 1.981 0.6728
Post-monsoon 2012 15 0.8695 2.231 0.8239
Cluster analysis on the basis of abundance of different species showed two main clusters (Fig. 3). First cluster consists of about 16 species whereas second cluster consists of 4species. First cluster is further divided into 2 sub clusters consisting of 11 and 5 species respectively. Out of 11 species 5 belong to the subgenus Sophophora whereas 3 species belong to subgenus Drosophila, 2 species belong to Genus Scaptodrosophila and one species belongs
to Genus Zaprionus. Out of 5 species present in the second sub cluster 4 belong to subgenus Sophophora while one species belong to subgenus Drosophila. The second cluster also consists of two sub clusters consisting of sympatric species D. malerkotliana and D. bipectinata belonging to subgenus Sophophora. D. n. nasuta belonging to subgenus Drosophila and P. striata belonging to Genus Phorticella are in the second sub cluster.
Fig 3: Cluster analysis of Drosophila species 4. Discussion
There is an effect of seasons on the population of Drosophila of Dharwad. They were more abundant during monsoon, less abundant during winter and moderate during summer and post- monsoon season. Few species which were found during monsoon season were rare and endemic. During monsoon, D. bipectinata, D.
malerkotliana, D. n. nasuta and P. striata were more dominant than other species. During post-monsoon and winter seasons, the population of these species decreased but they maintained their dominancy compared to other species. Present study agrees with the reports of Prakash and Reddy [22, 23]; Guruprasad et al. [8] and Achumi et al. [1] where majority of species collected belonged to melanogaster species group of the subgenus Sophophora and immigrans species group of the subgenus Drosophila indicating their sympatric association and ecological dominance [11]. During the months of summer, P. striata emerged as most successful species in summer as it is the mango fruit harvesting season in this area (Table 1). It is also reported that P. striata species is dependent on mango fruiting season during summer and decreases its abundance during other seasons. This fruit provides an excellent source of feeding and breeding site for the Drosophilids [28].
Fluctuations in tropical population sizes of Drosophila during different seasons are due to variations in the environmental factors such as rainfall, temperature and humidity [19]. Present study revealed that fluctuation in population densities of various species of Drosophila can be attributed to rainfall with more number of individual flies collected in monsoon compared to other seasons
and the size of the population decreases slowly by post-monsoon and reaches its lowest during dry winter season and again increases during summer. Torres and Madi – Ravazzi [29] reported that there is a positive correlation between population abundance and rainfall of three populations of Brazil. They have reported that populations of D. sturtevanti and D. malerkotliana were strongly influenced by rainfall. During the dry season, the number of individuals of both species was significantly reduced. Present study shows positive correlation between total abundance of species and rainfall (Fig. 1) and also among 12 individual species. D. melanogaster and D.
ananassae are considered as cosmopolitan species [20]. But these species showed no positive correlation with rainfall. Sympatric species D. bipectinata and D. malerkotliana coexisted during all the seasons in equal numbers and hence, justifies their adaptability to share the same habitat and maintain a successful reproductive isolation (Table 2).
Dobzhansky and Pavan [5] showed that rainfall has greater influence on the abundance of species than temperature. An increase in rainfall has direct influence on flowering and fruiting of plants, thus increasing the number of oviposition and feeding sites for the species [4]. Torres and Madi – Ravazzi [29] have reported no correlation between the total number of individuals captured and temperature among two out of three populations of Brazil. Present study also revealed that temperature has no relation with abundance of Drosophila population (Fig. 2).
Species richness alone has no effect on diversity indices [29]. Achumi et al. [1] have calculated Simpson’s index during the study
~ 40 ~
of seasonal variation of Drosophila from Mount Japfu. Their results revealed that species richness has no significant effect on diversity. Similar results were reported by Guruprasad et al. [8]
where a lower altitude region (680 m) with less number of species (18) was more diverse than higher altitude region (980 m) with more number of species (19). The Simpsons Index of diversity (1- D), Shannon Index revealed a greater diversity in the post-monsoon 2012 season even though monsoon 2012 season recorded maximum number of species (19). Minimum diversity was found in winter 2012 (Table 3). This may be more easily understood if we observe the quantity and dominance of each species collected during different seasons, Most of the flies collected during monsoon seasons were concentrated in just two species, D.
malerkotliana and D. bipectinata, which together represent 52.7%
of the whole sample collected. Whereas in post-monsoon season their population was stable and evenness maintained. Simpson’s Index is heavily dependent towards evenness and most abundant species in the sample and it is less sensitive to the species richness whereas Shannon index takes into account both species richness and abundance [13].
Eco-distributional analysis of Drosophila revealed that the distributional pattern of species or related group of species is uneven [1, 8]. Cluster analysis revealed that there are 2 major clusters of species, first cluster consisting of rare, endemic and cosmopolitan species which were found in less number where as the other sub cluster consists of intermediate species whose abundance is in between first sub cluster and second cluster. In the first cluster out of 16 species, 9 belonged to subgenus Sophophora which are morphologically related to each other thus indicating the coexistence of species having similar ecological preferences.
Second cluster is further divided into two sub clusters where one sub cluster consists of dominant sympatric species D.
malerkotliana and D. bipectinata. The other sub cluster consists of D. n. nasuta and P. striata which were also dominantly found species (Fig. 3).
5. Conclusion
The study revealed that Dharwad District is rich in Drosophila fauna endowed with rare and endemic species and further studies on species specific habitat/ microhabitat preferences will be very much helpful in understanding their ecological pattern and speciation.
6. Acknowledgement
The authors are thankful to the chairperson, Dept. of Zoology, Karnatak University, Dharwad for providing necessary facilities.
S.B.S. is thankful to UGC for award of Rajiv Gandhi National Fellowship and N.S to UGC MRP F. NO. 37/-241/2009 (SR) for financial assistance
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